In recent years, as size of LSI is getting smaller, a problem arises which is known as an optical proximity effect (OPE) that dimension change or shape change occurs between a pattern of an exposure mask and a pattern formed on a substrate (wafer). Therefore, optical proximity correction (OPC) where correction is applied to the mask pattern by taking into consideration influence of the optical proximity effect in advance is used.
As an OPC technique capable of obtaining a high correction accuracy, there is known a model-based OPC where an adjusting amount of an appropriate mask dimension is calculated based on lithography simulation. A model for the optical proximity correction is generated by adjusting model parameters such as acid diffusion of resist or mask shape so as to express the shape of mask pattern formed on the substrate. However, in the case where a measurement error of a critical dimension (CD) measurement value of the mask pattern is large, since the adjustment with respect to an abnormal value is also performed, reliability and accuracy of the model is lowered. Therefore, it is preferable that the accuracy of the simulation model is allowed to be improved by appropriately removing the abnormal value from the CD measurement values.